The electrical systems for which many electronic controllers are presently designed are typically, such as in automobiles, 12 V or 24 V systems. The controllers are typically attached to the car dashboard, seat bottom, or the like by being screwed into place.
Control of present-day electric motors, such as those used in the heating ventilating and air conditioning (HVAC) systems of automobiles, has mainly been achieved using switch-mode technology, in which a fixed power supply is turned on or off as needed to control the speed of the electric motor. In the United States, this technology has been implemented primarily by use of a resistive divider or by pulse width modulation (PWM). A resistive divider operates by modulating the power provided to the electric motor by a constant or adjustable amount, resulting in a choppy or stepwise level of control.
PWM works by modulating the timing of the lead and trail edges of the power signal to the electric motor. PWM results in a relatively inaccurate control of an electric motor, and may also introduce a choppy quality of control.
Alternatively, some use has been made in Europe of a type of linear motor controller. A linear electric motor controller generally works by directly controlling the motor speed by setting the voltage of the power supplied to the electric motor. The speed of the electric motor has a linear relationship with the voltage of the power supplied to the motor, hence the term “linear.” These systems are characterized by an undesirably large latency period, i.e., between detection and correction of the desired motor speed.
Also, some use has been made of analog variable-direct current (DC) voltage for control of variable speed electric motors, with a method that involves using a low-pass filter to generate the DC voltage. The low-pass filter used to generate the DC voltage to the motor introduces a stepwise/choppy quality to the control of the motor voltage, similar to the use of a resistive divider.
The widespread use of linear controllers for control of present-day variable speed electric motors, however, has been frustrated largely due to the large amount of heat generated by such controllers, and the difficulty thus encountered in practice when using such controllers. As an example, linear controllers may require heat dissipation ratings of 90-95 watts. Linear controllers used previously were designed so that the controller was remotely located from heat-sensitive structures, which tended to result in increased size of the controller module. The difficulty in cooling such linear controllers, thermal melting and breakdown of the material enclosing linear controller units, and a need for placement of the controller within a cooling air stream has limited the use of such controllers in practical applications.
On the other hand, PWM-type controllers require a heat dissipation rating of only 6-10 watts, which advantageously allows for the controller to be located adjacent to heat-sensitive components such as plastics. The housing of contemporary electric motor controller units, however, is typically made of standard injection-molded polypropylene plastics, which can handle close contact with 6-10 watts of heat dissipation as with a PWM-type controller, but not the 90-95 watts involved with linear controllers. Thus, switch-mode or PWM-type controllers tend to be highly desired for commercial production applications.
It would be desirable to overcome the various problems and disadvantages of both the heat-issues of linear control systems and the crude control of PWM-type controllers in the prior art to satisfy the design requirements for current electrical systems, in particular automotive systems.